Carcinogenicity and toxicity of four cadmium compounds inhaled by rats

This long-term inhalation study was designed to verify our previous results of the highly significant lung carcinogenicity of CdCl sub 2 aerosols. In addition, the study was expanded to include exposures in male and female rats to CdSO sub 4, CdS and CdO as fume and dust, and CdO dust combinations with ZnO dust. The rats were exposed to submicron Cd aerosols either continuously for up to 18 months, or discontinuously for 40 hours a week during a period of 6 months. Subsequently, groups of 20-40 rats were kept until death or up to the 31th month after beginning of the study. Highly significant lung tumor rates were found after continuous exposure to equal or bigger than 30 Myg/cubic meter Cd of all Cd compounds. There were even primary lung tumors after discontinuous CdO and CdS exposure for 40 hours weekly, but not after continuous exposure to 10 Myg Cd/cubic meter as CdO fume and 30 My g Cd/meter cube as CdO dust combined with 300 Myg Zn/cubic meter as ZnO dust. Flow cytometric analys is of the lung cell DNA was used as a method of early indication of lung carcinogenicity. The results obtained by this method were supported by those of bronchio-alveolar lavage and histopathological analyses showing correlations and suggesting that lung carcinogenicity of the Cd aeerosols is a result of Cd retention, of lung metallothionein induction, as well as of both the cytotoxic and proliferative effect of Cd to the respiratory tract of the rats.